1993 merc 70 hp force water in #2 cylinder

Anthony4261

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Sep 6, 2013
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Im a little stumped here. I am mechanically inclined but have yet to tackle any boat issues. My wife and I just bought our first boat and I'm having some issues. I'll start by giving the background. It ran perfectly for two days. I mean perfectly. I had two big guys on a tube behind me and hammered on the throttle. The boat really seemed to not move and was being held back by the tube. I let off and slowly got up to speed because the weight of the guys on the tube was a bit much for it I think. At that exact moment when I hit the throttle hard, the back of the boat went pretty low into the water and the motor started running horribly. It wouldn't idle anymore and would only go about 3/4 of top speed.

I pulled the plugs and found water droplets on the #2 cylinder. The plug looks very clean and the other two are brown as they should be. I did a compression test on all three cylinders and they are all within two psi of eachother and right around 120 psi. So the compression test is good.

So I am unsure where this water is coming from. Could it be that I sucked water through my exhaust when the boat went low into the water? I can't figure this out. It will run but will not idle and is obviously only running on two cylinders. It also starts very very hard. I am under the assumption there must be a bad gasket somewhere. I just have no clue where to begin. Thanks.

New to the forum and hoping to get some help. Any responses would be greatly appreciated. Please let me know if you need any other info. I tried to describe it as best as I could. Thanks again.
 

Cogburn

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Aug 24, 2010
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Re: 1993 merc 70 hp force water in #2 cylinder

I had one do the same thing and I have not yet put it together yet but the gasket under the powerhead was bad.
 

Anthony4261

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Re: 1993 merc 70 hp force water in #2 cylinder

Should I be concerened that I'm only seeing water in the #2 cylinder? Possibly bad rings?
 

Anthony4261

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Re: 1993 merc 70 hp force water in #2 cylinder

I tore off the carb today and shined a flashlight in there and noticed one of my reeds was basically gone. A peice of one of them is completely missing. Obviously this will make it run and start very hard.

Really hopin someone can point me in some kind of direction here. I'm assuming my power head seal is bad at this point but am clueless on where to even begin here. I'm taking the engine off tomorrow into my basement and dismantling it. Any advice is appreciated.
 

emckelvy

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Jan 16, 2004
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2,506
Re: 1993 merc 70 hp force water in #2 cylinder

I would replace the reed valve(s) first on the bad cylinder then see how it runs. I seem to recall something about a bad reed valve possibly causing that cylinder to suck water from the exhaust dump side. I can't recall exactly how that's supposed to work, but I'm sure it stuck in a few brain cells for a reason!

Anyway, nothing to lose, if it still doesn't run good after doing the reed valves, I'd maybe look to an issue with the exhaust manifold gaskets or inner baffle plate.

Of course another way to get water into the cylinders is with a bad head gasket, but with such even compression readings, it's not as likely. But if you can't find any other reason for the water ingestion, it may be necessary to pull the head and check anyway.

You'll want to have the head checked for flatness if you pull it.

Here's a link to some parts diagrams for your motor:

Force 70 HP (1991-1995) FUEL INTAKE SYSTEM Parts

HTH & G'luck with the repairs.
 
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